Surgical power tool and actuation assembly therefor

ABSTRACT

A surgical power tool has an actuation assembly for the actuation-force-dependent control of the tool. The actuation assembly includes a force sensor configured to sense the actuation force and a carrier component for the force sensor which is arranged upstream of the force sensor in a direction of force application and is coupled thereto in a force-transmitting manner. A mechanical damping member is arranged upstream of the carrier component in the direction of force application. The damping member protects the carrier component and the force sensor, for example, from impacts and shocks and the accompanying plastic deformations.

BACKGROUND OF THE INVENTION

The invention relates generally to surgical power tools such aselectric-motor-driven drills, bone saws and screwdrivers. To be moreprecise, the invention relates to a surgical power tool comprising anactuation assembly having a force sensor.

For several decades a wide variety of power tools have been used bysurgeons in their work. Conventional surgical power tools frequentlycomprise mechanical actuation assemblies having slide switches, tumblerswitches or rotary knobs for controlling certain functionalities of thetools. However, mechanical actuation assemblies are sometimesdisadvantageous for surgical power tools, if the tools have to besterilized at any rate. This is due to the fact that the movingcomponents of such assemblies are very difficult to seal against theingress of liquid or gaseous sterilization media.

The penetration of a sterilization medium into mechanical actuationassemblies is detrimental to their operability. For this reason,surgical power tools having tumbler switches, rotary knobs or similarmoving components either cannot be sterilized at all or must be servicedafter a few sterilization cycles.

To improve the sterilizability of surgical power tools, or to make itpossible in the first place, actuation assemblies may be equipped with aforce sensor. Force sensors have a planar design and have no movingmechanical elements. For these reasons, force sensors can be installedin a simple and sealed manner below a flexible housing section of asurgical power tool.

Surgical power tools having force sensors arranged below flexiblehousing sections are known, for example, from U.S. Pat. No. 3,463,990and U.S. Pat. No. 6,037,724. In the case of the power tools described inthese documents, the respective force sensor is housed within a casingof plastics material which protects the force sensor againststerilization media.

Furthermore, a surgical power tool having a force sensor arranged in ametal capsule is known from U.S. Patent Publication No. 2007/0096666,the disclosure of which is incorporated herein by reference. Theencapsulation protects the sensor reliably from sterilization media. Toensure the operability of the encapsulated force sensor, continuouscalibration is proposed.

The object on which the invention is based is to increase theoperability of known surgical power tools having force sensors.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, an actuation assembly for theactuation-force-dependent control of the operation of a surgical powertool is proposed, the actuation assembly comprising a force sensorconfigured to sense the actuation force, a carrier component for theforce sensor which is arranged upstream of the force sensor in adirection of force application and is coupled thereto in aforce-transmitting manner, and a mechanical damping member which isarranged upstream of the carrier component in the direction of forceapplication.

The mechanical damping member counteracts damage to the actuationassembly due to impacts or shocks in the surgical environment. For thispurpose, the damping member may have elastic or resilient properties.

With regard to the construction of the force sensor, a selection may bemade between different implementations. For example, it is possible toconfigure the force sensor as a strain gauge, a piezo element, asemiconductor element, etc. A signal processing circuit electricallycoupled to the force sensor may be provided for the force sensor.According to a first variant, the signal processing circuit taps asensor signal and converts it into a continuous output signal dependenton the actuation force. According to a second variant, the signalprocessing circuit converts the sensor signal into a discrete, i.e. forexample binary (On/Off) or multi-stage, output signal.

The force sensor may be completely or partially encapsulated. The sensorcapsule may be provided for arrangement in, on or under the housing ofthe surgical power tool. The capsule may consist wholly or partially ofa material resistant to sterilization media (or be coated with such amaterial). For instance, the capsule may be produced wholly or partiallyfrom a metal. The capsule may have a covering made of plastic or a coremade of a non-metallic material which is covered with a metal coating.The carrier component may be a part of the sensor capsule housing theforce sensor.

According to one variant, the actuation assembly further comprises a,preferably flexible, cover which is arranged above the carriercomponent. The damping member may in this case be either integrated intothe cover or arranged between the cover and the carrier component. It isalso conceivable to combine these two variants by arranging two or moredamping members one behind the other in the direction of forcetransmission.

The cover may have a substantially planar form and extend substantiallyperpendicularly to the direction of force application. Additionally oralternatively to this, the cover may also run substantially parallel tothe carrier component.

The damping member may have an, in particular convex, increase inthickness in places or be formed by an, in particular convex, increasein thickness of the cover in places. The increase in thickness in placespermits the definition of an application region for the actuation forcewhich is haptically readily detectable by the surgeon. The surgeon canthus feel the application region without necessarily having to look atthe actuation assembly or the surgical power tool.

According to one configuration, the damping member has a minimumthickness of approximately 1.5 mm and in particular of approximately 2to 2.5 mm. While the damping properties increase with increasingthickness, at the same time the force-transmitting properties may beimpaired. Despite the damping properties, the damping member may beformed with sufficient rigidity to be able to act as aforce-transmitting member in an arrangement in the force-transmittingpath between a force application region and the force sensor. Thethickness of the damping member may range between approximately 1.5 mmand 5 mm, in particular between 2 mm and 4 mm, depending on theconfiguration of the damping member and the choice of material.

Both the damping member and the optional cover may consist of a materialwhich is impervious to sterilization media. Elastic polymer materialssuch as silicone or other plastics may be used here.

The actuation assembly may be configured as an independently handleablesubassembly of the power tool. In this case, the actuation assembly maybe inserted as a whole (with its most important components at any rate)into a housing of the power tool, which simplifies assembly.

The actuation assembly may further comprise a support plate forreceiving the sensor capsule. The support plate may be configured toclose an opening, formed in a housing of the power tool, for receivingthe actuation assembly. The closing of the actuation assembly by thesupport plate may be effected in a fluid-tight manner in order tocounteract the ingress of a sterilization medium into the housinginterior. For this purpose, a seal may be provided between the supportplate and the housing section delimiting the opening.

To fix and/or center the sensor capsule on the support plate, a bearingcomponent at least partially surrounding the sensor capsule may be used.For this purpose, the bearing component may have a receiving opening forthe sensor capsule. The support plate and the bearing component may beproduced in one piece or as separate components.

According to a further aspect, a surgical power tool which comprises ahousing and an actuation assembly as described here which is arranged inthe region of the housing is proposed. The surgical power tool mayfurther comprise an electric motor for the actuation of a tool element(e.g. a screwdriver blade, a saw blade, a drill bit, etc.). In addition,it is conceivable for the surgical power tool to have more than oneactuation assembly.

The housing of the power tool may have an opening for the application offorce in the direction of the force sensor. The cover can close theopening in a manner sealed against the ingress of sterilization media.For this purpose, the cover may, in the course of assembly, be subjectedto a force which compresses the cover and which is maintained in thefinished, assembled state. Furthermore, it is possible for the cover tohave a first surface profiling which surrounds the opening of thehousing and which cooperates in a substantially form-fitting manner witha second surface profiling of the housing. The form fit resulting inthis case can form a barrier to the ingress of sterilization media.

Furthermore, the cover may be arranged sealingly between a first surfaceof the housing facing into the housing interior and a second surface ofthe actuation assembly facing the first surface. The first surface maybe an undercut or a projection of the housing. The second surface may beformed on a bearing component for the carrier component.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and advantages of the invention will become apparentfrom the following description of preferred exemplary embodiments andfrom the figures, in which:

FIG. 1 shows a top view of an exemplary embodiment of a surgical powertool in the form of a screwdriver;

FIG. 2 shows a partial-sectional view of the surgical power toolaccording to FIG. 1 along the line A-A;

FIG. 3 shows an enlargement of the detail Z of the sectional viewaccording to FIG. 2, illustrating in particular an exemplary embodimentof an actuation unit comprising two actuation assemblies;

FIG. 4 shows a schematic partial-sectional view of a sensor capsule ofone of the actuation assemblies according to FIG. 3;

FIG. 5 shows a sectional view of a housing of the sensor capsuleaccording to FIG. 4;

FIG. 6 shows a top view of a force sensor used in each of the actuationassemblies according to FIG. 3, in the form of a strain gauge;

FIG. 7 shows an enlargement of the detail Y of the sectional viewaccording to FIG. 3, illustrating in particular the operation of aswitch;

FIG. 8 shows a perspective view of a spring plate used in the switchaccording to FIG. 7;

FIG. 9 shows a side view of the spring plate according to FIG. 8; and

FIGS. 10A/B show a schematic flow chart, illustrating an exemplaryembodiment of a method for operating the surgical power tool.

DETAILED DESCRIPTION

Exemplary embodiments of surgical power tools, of an actuation assemblyprovided therefor, and of an operating method suitable therefor areexplained below. Corresponding elements are provided with correspondingreference symbols.

FIG. 1 shows a plan view of a surgical power tool 10 in the form of abattery-operated screwdriver. The surgical power tool 10 has anelongated, approximately cylindrical housing 12 made of aluminium, ontothe rear side of which a battery pack (shown only schematically and inbroken lines) can be plugged removably.

In the exemplary embodiment, the surgical power tool 10 comprises twoactuation assemblies 14, 14′ for controlling different tool functions.The actuation assemblies 14, 14′ are provided in a front region of thehousing 12 which is remote from the battery pack. As can be seen inparticular from the sectional view illustrated in FIG. 2 along the lineA-A of FIG. 1, the actuation assemblies 14, 14′ are received in a collar16 of the housing 12 which projects from a cylindrical wall region 18 ofthe housing 12. The collar 16, which is produced in one piece with thewall region 18, surrounds the actuation assemblies 14, 14′ laterally andprotects them from mechanical influences. On its upper side, the collar16 has two circular openings 16A, 16A′ in order to allow a user toaccess the actuation assemblies 14, 14′.

As shown in FIG. 2, an assembly 20 having an electronically commutatedmotor 22 and a transmission 24 coupled to the motor 22 is provided inthe interior of the housing 12. A first of the two actuation assemblies14, 14′ controls the electric motor 22 in a first direction of rotation.The other of the actuation assemblies 14, 14′ controls the electricmotor 22 in a second direction of rotation opposite to the firstdirection of rotation. The motor speed in the forward and reversedirections is regulated in each case proportionally to the actuationforce applied to the respective actuation assembly 14, 14′. The higherthe actuation force, the higher is therefore the motor speed. Toregulate the speed, a motor control circuit is provided on a printedcircuit board (not shown) fixed in the rear portion of the housing 12.

In addition, a coupling 26 is housed in the housing 12 downstream of thetransmission. The coupling 26 permits in known fashion the rotationallyfixed coupling of an exchangeable screwdriver blade (not shown) to thetransmission 24. An optional locking button (likewise not shown) enablesrotationally fixed mechanical locking of the coupling 24. When thelocking button is actuated, the power tool 10 can be used in the mannerof a conventional screwdriver. In this case, the torque is not generatedby the motor 22 but by manual rotation of the housing 12.

The total of two actuation assemblies 14, 14′ of the surgical power toolhave the same construction and together form an actuation unit 28 whichcan be handled independently and inserted as a subassembly into thehousing 12. FIG. 3 shows the actuation unit 28 in an enlargement of thedetail Z of the sectional view according to FIG. 2.

As can be seen in FIG. 3, the actuation assemblies 14, 14′ each comprisea sensor capsule 30, 30′ made of metal for hermetic encapsulation of arespective force sensor (not shown in FIG. 3). The sensor capsules 30,30′ are arranged on a common support plate 32 which closes a housingopening formed on the lower side of the collar 16. The sensor capsules30, 30′ are fixed on the support plate 32 by means of a common bearingcomponent 34 which centers the sensor capsules 30, 30′. For thispurpose, the bearing component 34, of block-shaped form, has twocylindrical bores 36, 36′ for receiving a respective sensor capsule 30,30′. The bearing component 34 consists of an insulating material such asplastic or is otherwise electrically insulated from the metal sensorcapsules 30, 30′.

The bores 36, 36′ in the bearing component 34 are formed asthrough-openings and permit access to electrical contacts of the sensorcapsules 30, 30′ from below and the application of an actuation force tothe sensor capsules 30, 30′ from above. Furthermore, the bores 36, 36′have a stepped profile with a respective circumferential shoulder 38,38′ which acts as a seat for a diameter enlargement 40, 40′ of eachsensor capsule 30, 30′. Provided between each shoulder 38, 38′ anddiameter enlargement 40, 40′ is a seal 42, 42′ in the form of a siliconering. The seals 42, 42′ prevent the ingress of a sterilization mediumalong the side walls of the sensor capsules 30, 30′ and the inner wallsof the bores 36, 36′ in the direction of the support plate 32 and theinterior of the tool housing 12. In addition, the seals 42, 42′ centerthe sensor capsules 30, 30′ on the mounting of the latter in the bearingcomponent 34. For this purpose, the seals 42, 42′ may have a suitableprofiling (e.g. a thickness decreasing in the direction of the axis ofthe bores 36, 36′).

Provided on the upper side of the bearing component 34 are a planarspring plate 44 and an elastic cover 48 made of silicone or anothersuitable material. The cover 48 is arranged sealingly between anundercut of the collar 16 and an upper side of the bearing component 34and thus prevents the ingress of sterilization media through the housingopenings 16A, 16A′ into the interior of the collar 16 and into the toolhousing 12.

In order to optimise the sealing action, the cover 48 has a plurality ofsurface profilings arranged concentrically with respect to the housingopenings 16A, 16A′ (in FIG. 3, only a single surface profiling 48B ismarked, for the sake of clarity). The surface profilings of the cover 48are formed as circular projections and cooperate in a form-fittingmanner with assigned surface profilings of the collar 16 and of thebearing component 34 in the form of corresponding indentations. The formfit which thus results counteracts the ingress of sterilization media ina direction parallel to the cover 48.

In order to protect the sensor capsules 30, 30′ (and the force sensorshoused therein) from impacts and shocks in the surgical environment,each of the two actuation assemblies 14, 14′ has a respective mechanicaldamping member 48A, 48A′ which is arranged upstream of the sensorcapsules 30, 30′ in the direction of force application. The direction offorce application is illustrated in FIG. 3 by a block arrow for each ofthe actuation assemblies 14, 14′.

The mechanical damping members 48A, 48A′ are integrated into the cover48 in the exemplary embodiment shown in FIG. 3. To be more precise, thedamping members 48A, 48A′ are formed as convex increases in thickness ofthe cover 48 above the central region of each of the two sensor capsules30, 30′. Owing to the convex shaping, the damping members 48A, 48A′define a region of application for the actuation force which ishaptically readily detectable by the user. In the exemplary embodimentaccording to FIG. 3, the damping members 48A, 48A′ have a materialthickness of approximately 2.5 to 3.5 mm in their thickest region.

As can be seen in FIG. 3, the spring plate 44 is arranged between thecover 48 and the upper sides of the sensor capsules 30, 30′. Withrespect to each of the two actuation assemblies 14, 14′, the springplate 44 is part of respective switch 46, 46′. To be more precise, thespring plate 44 provides a respective first contact for each switch 46,46′. The respective second switching contact is provided by the (metal)upper sides of the sensor capsules 30, 30′. In the first switching stateof the switches 46, 46′ shown in FIG. 3, the two respective switchingcontacts are kept spaced apart from one another by the spring force ofthe spring plate 44. The two switches 46, 46′ are thus in an openswitching state.

In what follows, the construction of the sensor capsules 30, 30′ and ofthe switches 46, 46′ is explained in more detail with reference to FIGS.4 to 9. FIG. 4 shows a partial-sectional view of the sensor capsule 30of the actuation assembly 14. The capsule 30 has a substantiallypot-shaped cap 50 made of special steel, which is shown againindividually in FIG. 5. The cap 50 comprises a cylindrical wall section52 and a cover section 54 formed in one piece with the wall section 52.The internal diameter of the wall section 52 is approximately 11 mm(typically approximately 5 to 30 mm) and the height of the wall section52 is approximately 7 mm (typically approximately 2 to 12 mm). The coversection 54 closes the, in FIG. 4 upper, end side of the wall section 52.The open lower end side of the cap 50 is closed by a cap base 56hermetically against sterilization media. The cap base 56 likewiseconsists of special steel.

A plurality of through-openings (not shown) are formed in the cap base56. A gold-plated electrical contact 58 extends through eachthrough-opening. To stabilise the contacts 58 on the one hand and toensure a high degree of sealing on the other hand, the openings in thecap base 56 are hermetically closed by means of glass.

While the cover section 54 has a thickness of approximately 0.3 mm atmost, the wall section 52 has a thickness of at least approximately 0.8mm or more (cf. FIG. 5). Such a design is advantageous in restricting tothe cover section 54 the elastic deformation resulting from applicationof an actuation force to the cover section 54. In other words, the wallsection 52 behaves in a substantially rigid manner with respect to theactuation force applied to the cover section 54. This facilitates thehermetically sealed installation of the sensor capsule 30 in theactuation assembly 14 and in the housing 12 of the power tool 10.

A force sensor 60 and a signal processing circuit 62 for the forcesensor 60 are housed inside the capsule 50. FIG. 6 shows a top view ofthe force sensor 60. The force sensor 60 comprises a planar strain gaugeconfigured in meandering form and having two contacts 64, 66. In thefinished, mounted state, the contacts 64, 66 are electrically connectedto the signal processing circuit 62. Mounting of the force sensor 60flat on the inner side of the cover section 54 can be effected byadhesive bonding.

As shown in FIG. 4, the force sensor 60 is coupled to the signalprocessing circuit 62 by means of electrical contactings 68, 70. Thesignal processing circuit 62 is in turn electrically contacted by thecontacts 58 leading out of the capsule 30.

The construction of the switches 46, 46′ is now described with referenceto FIGS. 7 to 9. In this regard, reference is first made to FIG. 7 andthe enlargement of the detail Y in FIG. 3 shown there. The constructionof the switch 46 from a first switching contact 44A formed on the springplate 44 and from a second switching contact formed by the metal coversection 54 of the sensor cap 50 can be clearly seen in FIG. 7.

As can be seen from the shaping of the spring plate 44 illustrated inFIG. 8, the switching contact 44A of the switch 46 is formed by atongue-shaped spring plate section which is connected at one location toan annular further spring plate section. The annular spring platesection lies on the bearing component 34 shown in FIG. 3, while thetongue-shaped spring plate region (with the switching contact 44A) isdeflectable perpendicularly to the plane of the spring plate against aspring force. This deflection takes place in an elastically reversiblemanner, so that following a deflection the spring plate 44 assumes itsoriginal planar form again.

FIG. 9 shows a side view of the spring plate 44. The rolling directionduring production of the spring plate 44 is further indicated in FIG. 9by an arrow. The spring plate 44 is coated on both sides with anelectrically insulating material such as, for example, parylene. Onlythree contact locations are left free from this coating, namely theswitching contact 44A, a corresponding switching contact 44B of thesecond actuation assembly 14′ and a contact region which is formed inthe center of the spring plate 44 and via which a circuit is closed. Asshown in FIGS. 7 and 9, the switching contact 44A has a concavely curvedshape in order to establish a defined, point contact closure between theswitching contact 44A and the switching contact lying opposite in FIG. 7in the form of the cover section 54.

The operation of the actuation assembly 14 is now explained in moredetail with reference to FIGS. 3, 4 and 7. It will be understood thatthe following statements also apply to the operation of the secondactuation assembly 14′.

When an actuation force is applied (for example by finger pressure) tothe readily palpable thickened section 48A of the elastic cover 48, thelatter is displaced in the direction of the housing interior. Alsoinvolved in this displacement of the cover 48 is the switching contact44A shown in FIG. 7, which in the initial state lies against the cover48. To be more precise, the switching contact 44A is displaced in thedirection of the cover section 54 against the spring force provided bythe spring plate 44. After a displacement travel of approximately 0.5 mm(typically about 0.1 to 2 mm), the switching contact 44A comes intocontact with the cover section 54. As a result of this coming intocontact, the switch 46 is closed, i.e. it is transferred from an openstate to a closed state. The closing of the switch 46 at the same timecauses the closing, detectable by means of a logic circuit, of a circuitcomprising the spring plate 44 and the sensor capsule 30 as conductingelements. In an alternative embodiment (not shown), the switch 46 isconfigured to be opened by the actuation force.

As soon as the switching contact 44A has come into contact with the capcover 54, a further increase of the actuation force causes an actuationforce component to be applied to the cover section 54. The upper side ofthe cover section 54 permits the take-up of this actuation forcecomponent. The cover section 54 thereupon deforms elastically in thedirection of the interior of the capsule 30. This deformation of thecover section 54 is transmitted to the force sensor 60, which isfastened to the lower side of the cover section 54 (cf. FIG. 4). To bemore precise, the deformation causes stretching of the force sensor 60configured as a strain gauge. As a result of this stretching, theresistance of the force sensor 60 changes. This change of resistance ofthe force sensor 60 in turn displaces the operating point of a bridgecircuit which comprises the force sensor 60 and together with anamplifier circuit forms the signal processing circuit 62. The forcesensor 60 is part of the bridge circuit, which, in addition to threefurther bridge resistors, also comprises two balancing resistors. Asuitable circuit is known, for example, from U.S. Patent Publication No.2007/0096666.

The displacement of the operating point is detected by the amplifiercircuit, in the form of a differential amplifier, of the signalprocessing circuit 62 and converted into an amplified difference signal.The amplified difference signal is provided by the signal processingcircuit 62 as an output signal for further processing. The level of theoutput signal is proportional to the deformation of the strain gauge andtherefore also proportional to the actuation force applied to the coversection 54. In an alternative embodiment, the signal processing circuitis so configured that the output signal has two or more discrete levels(for example, in dependence on the exceeding of one or more forcethresholds).

A motor control circuit is electrically coupled to the signal processingcircuits of the actuation assemblies 14, 14′. A logic circuit isarranged functionally between the motor control circuit and the twoactuation assemblies 14, 14′. The logic circuit has essentially theeffect that with simultaneous application of force to both actuationassemblies 14, 14′ no undefined state is produced. For this purpose thelogic circuit has two separate input connections, each of which iscoupled to one of the two actuation assemblies 14, 14′. If a signal issupplied to only one of the two input connections, an amplified outputsignal is transmitted to the motor control circuit via exactly one oftwo output connections. A signal for the first direction of rotation issupplied to the motor control circuit via a first control connection anda signal for the second, opposite direction of rotation via a secondcontrol connection.

If output signals are supplied to both input connections of the logiccircuit (i.e. if an actuation force is applied to both actuatingassemblies 14, 14′), the logic implemented in the logic circuit causesno output signal to be delivered from either of the two outputconnections to the motor control circuit. In addition, a “brake”connection assumes a high signal level. The high signal level at the“brake” connection short-circuits the electronically commutated electricmotor 22, whereby the electric motor 22 is electrically braked andbrought to a standstill. The logic circuit also comprises a speedregulation output. Via the speed regulation output, the motor controlcircuit receives feedback regarding the required motor speed. A suitablelogic circuit is known, for example, from U.S. Patent Publication No.2007/0096666. The known logic circuit may be further supplemented withlogic elements which link the output signals of the switches 46, 46′ andof the output connections explained above (e.g. by means of an ANDoperation), in order to implement the plausibility check explainedbelow.

In what follows, the operation of the surgical power tool 10 isdescribed in more detail with the aid of the schematic flow chart 100according to FIGS. 10A and 10B. The operating method begins in step 102with the plugging of a battery pack onto the tool base body shown inFIG. 1 and the accompanying initialisation of the individual toolcircuits in step 104. Following the initialisation step 104 and awaiting time (step 106), the operability of the two switches 46, 46′(also called main switches or “MSW” below) is checked in step 108. Thisinvolves in particular checking whether both switches 46, 46′ are intheir open switching state shown in FIG. 3. If one of the two switches46, 46′ is in a closed switching state already in the initializationstate of the power tool 10, this indicates a malfunction (for example abent spring plate 44 or fluid ingress).

At the same time as or at a time interval from the testing of theswitches 46, 46′, the force sensor signals of the actuation assemblies14, 14′ are read out in step 110. In a following checking step 112, itis determined whether the output signals of the force sensors lie withina preset range (e.g. above preset lower limits and below preset upperlimits). Undershooting a lower limit or overshooting an upper limit inthe initialization state indicates a malfunction (for example a plasticdeformation of a cover section 54). If it is established in step 112that the lower limit is undershot or the upper limit is overshot for atleast one of the force sensors or that one of the switches 46, 46′ is ina closed state, the method branches to step 114 and operation of thepower tool 10 is blocked. An acoustic signal indicating the malfunctioncan be simultaneously emitted.

If, in contrast, no malfunction is found in step 112, the methodcontinues with a checking step 116. In step 116 it is determined whethera first timer, which has been started for example during a precedingoperating process or in the initialisation step 104, has elapsed. If itis established in step 116 that the first timer has elapsed, the methodbranches to step 118 and a temperature sensor arranged in the housinginterior is read out. The temperature sensor is arranged on the printedcircuit board of the motor control circuit close to thetemperature-sensitive electronic components. Subsequently, the read-outtemperature value is compared with a temperature upper limit T_(max) offor example 80° in the checking step 120. In general, the temperatureupper limit may lie in a range between 60° and 100°.

If the temperature value lies above the temperature upper limit, in step122 the operation of the power tool 10 is temporarily blocked to preventfailure or destruction of electronic components. Simultaneously, thetemporary blockage of the operation is indicated by an acoustic signal(which differs from the acoustic signal of step 114). Then, in steps 124and 126 the temperature is read out once again and compared with thetemperature upper limit T_(max). The two steps 124 and 126 are carriedout until the temperature upper limit is no longer overshot. As soon asthis case occurs, the method branches from step 126 back to step 102.

If, on the other hand, in step 120 it is established that thetemperature upper limit is not overshot, or the first timer (step 116)has not yet elapsed, the operating method is continued with a step 128in which a second timer is read out. The second timer, which waslikewise started for example with the last operating process or in theinitialisation step 104, presets the valid period of time for an earliersensor calibration. If it is determined that this period of time haselapsed, a recalibration of the force sensors is carried out in step130. The recalibration in step 130 can take into account the forcevalues read out in step 110 and include an adaptation, based on theseforce values, of the corresponding upper limits for the checking in step112. If it is determined in step 128 that no recalibration is required,or if a recalibration has been carried out in step 130, the operatingmethod is continued with step 132.

In step 132 the force sensors of the two actuation assemblies 14, 14′are read out again. As already explained above, a first actuationassembly 14 controls the drive of the electric motor 22 in a firstdirection of rotation (“FWD”), while the second actuation assembly 14′controls the operation of the electric motor 22 in the oppositedirection of rotation (“REV”).

After the sensor values have been read out in step 132, it is checked instep 134 whether the force sensor of the actuation assembly 14 deliversan actuation signal (“FWD”). If this is the case, it is determined in afollowing step 136 whether the force sensor of the other actuationassembly 14′ likewise delivers an actuation signal (“REV”). If it isestablished in steps 134 and 136 that the force sensors of bothactuation assemblies 14, 14′ deliver actuation signals, it is concluded,as explained above, that an undefined actuation state is present, sinceboth actuation assemblies 14, 14′ are actuated. Thereupon, in step 138braking of the electric motor 22 takes place as discussed above inconnection with the logic circuit. If the electric motor 22 is still notrunning at all, the electric motor 22 remains in this state. Followingstep 138, the two timers for the temperature check and the checking fora required recalibration are reset in step 140. The operating methodthen branches back to step 116.

If it is established in step 134 that the force sensor of the actuationassembly 14 has not been pressed and if, furthermore, it can bedetermined in step 142 that the force sensor of the further actuationassembly 14′ has not been pressed either, braking of the electric motor22 takes place in step 144 analogously to step 138, and the methodcontinues with the checking step 116. If, in contrast, it is determinedin the steps 136, 142 that only one of the two force sensors of theactuation assemblies 14, 14′ delivers an actuation signal, it is checkedin step 146 whether an operating mode has been selected in which aplausibility check of the force sensor signals by means of the switchingstate of the switches 46, 46′ has been selectively deactivated. In thecase of a deactivated plausibility check, the operating method branchesfrom step 146 to step 148, and the electric motor 22 is started in therequired direction of rotation (“FWD”/“REV”). The motor speed is thenregulated in dependence on the signal delivered by the correspondingactuation assembly 14, 14′ (i.e. in dependence on the actuation force).

If, on the other hand, it is established in step 146 that an operatingmode is activated in which a plausibility check takes place byevaluation of the switching state of the corresponding switch 46, 46′,it is determined in the steps 150 and 152 whether the switch 46, 46′which is assigned to the actuation assembly 14, 14′ delivering theactuation signal is in its closed switching state. If this is not thecase, this points to a malfunction since it is not plausible that, whenthe switch 46, 46′ is open, the force sensor of the assigned actuationassembly 14, 14′ delivers an actuation signal. For this reason, themethod in this case branches from step 152 to step 138 and the electricmotor 22 is braked or not even started at all.

If, on the other hand, in the course of the plausibility check in step152 it is determined that the switch 46, 46′ which is assigned to theactuation assembly 14, 14′ delivering the actuation signal is in itsclosed state, the plausibility check is successfully concluded and theelectric motor is started in step 148 in the required direction ofrotation. In addition, its speed is regulated in dependence on theactuation force.

The surgical power tool 10 described affords increased operationalreliability owing to the switches 46, 46′ provided in addition to theforce sensors, since implausible operating states can be reliablydetected. Such implausible operating states may be accompanied, forexample, by a plastic deformation of the sensor capsules 30, 30′ due toshocks or impacts. To be precise, in the event of a plastic deformation,the associated force sensor may deliver a signal which could beerroneously interpreted as an actuation signal. However, the evaluationof the switching state of the switches 46, 46′ is not restricted to theplausibility check explained above.

In order to avoid a plastic deformation of the sensor capsules 30, 30′as far as possible, a mechanical damping member 48A, 48A′ is arrangedupstream of each sensor capsule 30, 30′ in the direction of forceapplication. In the exemplary embodiment described here, the dampingmembers 48A, 48A′ are integrated, as convex increases in thickness, intothe cover 48 and thus define a haptically readily detectable forceapplication region. In other embodiments, it would be conceivable toprovide the damping members below the cover 48 (e.g. between the cover48 and each sensor capsule 30, 30′).

Further advantages of the power tool 10 described here consist in theimproved sealing of the housing interior with respect to sterilizationmedia. This improved sealing is attributable, for example, to theprovision of additional sealing elements such as the annular seals 42,42′ and to the sealing function of the cover 48 and the support plate32. Further advantages result from the overall increased stability ofthe actuation assemblies 14, 14′ which is attributable, inter alia, tothe use of the support plate 32 and the bearing component 34. It isobvious to a person skilled in the art that these variousfunctionalities and advantages may be realised independently of oneanother. Thus, for example, the improved sealing functions and theincreased stability can be realised independently of the use of theswitches 46, 46′.

Self-evidently, the field of application of the actuation assemblypresented here is not limited to a surgical power tool in the form of ascrewdriver. Rather, an actuation assembly can also be used in othersurgical power tools, such as drills, saws, etc.

Numerous modifications and additions relating to the actuation assemblyaccording to the invention and to the surgical power tool according tothe invention are therefore possible. The scope of the invention islimited solely by the range of protection of the following claims.

The invention claimed is:
 1. An actuation assembly for anactuation-force-dependent control of the operation of a surgical powertool, comprising: a force sensor capsule capable of being mounted in anopening of a housing of the power tool; a force sensor arranged in theforce sensor capsule configured to sense the actuation force; the forcesensor capsule having a metal first cover section which is arrangedproximal of the force sensor in a direction of force application and iscoupled thereto in a force-transmitting manner, wherein the force sensoris configured to detect a deformation of the metal first cover sectionand wherein the force sensor is hermetically sealed againststerilization media; a mechanical damping member which is arranged on anouter surface of the metal first cover section in the direction of forceapplication, the mechanical damping member formed of an elasticmaterial; a spring plate disposed between the mechanical damping memberand the metal first cover section, wherein the spring plate is spacedapart from the metal first cover section in an undeflected state, andwherein application of the actuation force to the mechanical dampingmember deflects the spring plate toward the first cover section; andwherein the spring plate has an upper surface and a lower surface and aswitching contact surface, both the upper and lower surfaces are coatedwith an electrically insulating material, with the switching contactsurface free of the insulating material.
 2. The actuation assemblyaccording to claim 1, further comprising a second cover which isarranged above the sensor capsule, the damping member is integrated intothe second cover or arranged between the second cover and the sensorcapsule.
 3. The actuation assembly according to claim 2, wherein thesecond cover extends substantially perpendicularly to the direction offorce application and substantially parallel to the sensor capsule. 4.The actuation assembly according to claim 1, wherein the damping memberhas an increased thickness at a central protrusion above the metal firstcover section versus areas surrounding the protrusion.
 5. The actuationassembly according to claim 4, wherein the increase in thickness ishaptically detectable application region for the actuation force.
 6. Theactuation assembly according to claim 1, wherein the damping member hasa minimum thickness of about 1.5 mm.
 7. The actuation assembly accordingto claim 1, wherein the damping member is impervious to sterilizationmedia.
 8. The actuation assembly according to claim 1, wherein thedamping member contains an elastic polymer material.
 9. The actuationassembly according to claim 1, wherein the force sensor capsulecomprises a cap, the metal first cover section is formed by a section ofthe cap, and the force sensor is disposed at least partially inside thecap.
 10. The actuation assembly according to claim 1, wherein theactuation assembly forms an independently handleable subassembly of thepower tool.
 11. The actuation assembly of claim 1, wherein the springplate comprises an annular section and a tongue-shaped section connectedto the annular section, wherein application of the actuation force tothe mechanical damping member deflects the tongue-shaped section towardthe metal first cover section.
 12. The actuation assembly of claim 1,further comprising a collar arranged around the opening in the housinglaterally surrounding the sensor capsule.
 13. The actuation assembly asset forth in claim 1, wherein the spring plate has a deflectable portionextending towards a central portion of the force sensor capsule.
 14. Theactuation assembly as set forth in claim 1, wherein the spring plate hasa circumferential outer portion spaced apart from the metal first coversection along the entire circumferential outer portion.
 15. A surgicalpower tool, comprising a housing; an actuation assembly mounted on thehousing comprising: a force sensor configured to sense an actuationforce; a sensor capsule mounted in an opening in the housing and holdingthe force sensor, the sensor capsule having a first cover section whichis arranged proximal of the force sensor in a direction of forceapplication and is coupled thereto in a force-transmitting manner; amechanical damping member which is arranged outside of the first coversection in the direction of force application; a spring plate disposedbetween the mechanical damping member and the first cover section,wherein the spring plate is spaced apart from the first cover section inan undeflected state, and wherein application of the actuation force tothe mechanical damping member deflects the spring plate toward the firstcover section; and wherein the spring plate has an upper surface and alower surface and a switching contact surface, both the upper and lowersurfaces are coated with an electrically insulating material, with theswitching contact surface free of the insulating material.
 16. Thesurgical power tool according to claim 15, further comprising a secondcover which is arranged above the sensor capsule, wherein the dampingmember is integrated into the second cover or arranged between thesecond cover and the sensor capsule wherein the housing has an openingfor the application of force in the direction of the force sensor, thesecond cover closing the opening in a manner sealed against the ingressof sterilization media.
 17. The surgical power tool according to claim16, wherein the second cover has a first surface profiling whichsurrounds the opening of the housing and which cooperates in aform-fitting manner with a second surface profiling of the housing. 18.The surgical power tool according to claim 16, wherein the second coveris arranged sealingly between a first surface of the housing facing intoa housing interior and a second surface of the actuation assembly facingthe first surface.
 19. The surgical power tool according to claim 18,wherein the first surface is formed on a projection of the housing andthe second surface is formed on a bearing member for the sensor capsule.20. The actuation assembly of claim 15, wherein the spring platecomprises a switching contact, wherein the application of the actuationforce deflects the switching contact into contact with the metal firstcover section, and wherein the contact of the switching contact with themetal first cover section switches an electric switching circuit.
 21. Asurgical power tool, comprising: an elongated housing, having a firstend and a second end, wherein a coupling for a tool element is providedat the first end of the housing and a battery pack is provided at thesecond end of the housing; an electric motor provided in an interior ofthe housing for an actuation of the tool element; a motor controlcircuit provided in the interior of the housing, wherein the motorcontrol circuit is electrically connected to the electric motor and tothe battery pack; at least one actuation assembly for anactuation-force-dependent control of the operation of the surgical powertool, the at least one actuation assembly being electrically connectedto the motor control circuit and being arranged in an opening of thehousing, the at least one actuation assembly comprising a sensor capsuleand a force sensor arranged in the sensor capsule, the sensor capsulecomprises a wall section, a cap base, and a cover section made of metal,wherein the force sensor is mounted on the metal cover section and isconfigured to detect a deformation of the metal cover section, andwherein the force sensor is hermetically sealed against sterilizationmedia; a mechanical damping member which is arranged on the outside ofthe metal cover section in a direction of force application; a metalspring plate engaging a surface of the mechanical damping member,wherein the metal spring plate is located between the metal coversection and the mechanical clamping member and, in an undeflected state,is spaced apart from the cover section in the direction of forceapplication; wherein the housing further comprises a collar, which isarranged around the opening to laterally surround the sensor capsule;and wherein the spring plate has an upper surface and a lower surfaceand a switching contact surface, both the upper and lower surfaces arecoated with an electrically insulating material, with the switchingcontact surface free of the insulating material.
 22. The surgical powertool according to claim 21, wherein the actuation assembly comprises aswitch having a first contact and a second contact, the first contactand the second contact being kept spaced apart from one another by aspring force in a first switching state.
 23. The surgical power toolaccording to claim 21, wherein the mechanical damping member engages aspring element producing a spring force.
 24. The surgical power toolaccording to claim 23, wherein the mechanical damping member has athickened portion having a convex surface engaging the spring element.25. The actuation assembly of claim 21, wherein the spring platecomprises a switching contact, wherein the application of the actuationforce deflects the switching contact into contact with the metal firstcover section, and wherein the contact of the switching contact with themetal first cover section switches an electric switching circuit.
 26. Anactuation assembly for an actuation-force-dependent control of theoperation of a surgical power tool, comprising: a force sensor capsulecapable of being mounted in an opening of a housing of the power tool; aforce sensor arranged in the force sensor capsule configured to sensethe actuation force; the force sensor capsule having a metal first coversection which is arranged proximal of the force sensor in a direction offorce application and is coupled thereto in a force-transmitting manner,wherein the force sensor is configured to detect a deformation of themetal first cover section and wherein the force sensor is hermeticallysealed against sterilization media; a mechanical damping member which isarranged on an outer surface of the metal first cover section in thedirection of force application, the mechanical damping member formed ofan elastic material; a spring plate disposed between the mechanicaldamping member and the first cover section, wherein the spring plate isspaced apart from the first cover section in an undeflected state, andwherein application of the actuation force to the mechanical dampingmember deflects the spring plate toward the first cover section; whereinthe spring plate comprises a switching contact, wherein application ofthe actuation force deflects the switching contact into electricalcontact with the metal first cover section, and wherein the electricalcontact of the switching contact with the metal first cover sectionswitches an electric switching circuit; and wherein the spring plate hasan upper surface and a lower surface and a switching contact surface,both the upper and lower surfaces are coated with an electricallyinsulating material, with the switching contact surface free of theinsulating material.